This invention generally relates to golf balls, and more particularly, to a golf ball with an improved core.
Conventional golf balls have been designed to provide particular playing characteristics. These characteristics are generally initial velocity, compression, and spin of the golf ball, which can be optimized for various types of players. For instance, certain players prefer a ball that has a high spin rate in order to control the ball flight and stop the golf ball on impact with the greens. This type of ball, however, does not provide maximum distance. Other players prefer a ball that has a low spin rate and high resiliency to maximize distance.
Generally, golf balls have been classified as wound balls or solid balls. Wound balls are generally constructed from a liquid or solid center surrounded by an elastic thread wound in tension to form a wound core. This wound core is then surrounded by a cover. Wound balls are generally thought of as performance golf balls, not distance balls. When struck by a golf club, these balls have good resiliency, relatively high spin rate, and xe2x80x9csoftxe2x80x9d feel. Wound balls are generally more difficult to manufacture than solid golf balls.
Early solid golf balls were generally comprised of a hard core and a hard cover. However, if the golf ball has a soft core and a hard cover, it has a low spin rate. If the golf ball has a hard core and a hard cover, it exhibits very high resiliency for distance, but a xe2x80x9chardxe2x80x9d feel and is difficult to control on the greens. Additionally, if the golf ball has a hard core and a soft cover, it will have a high rate of spin. More recently developed solid balls are comprised of a core, at least one intermediate layer, and a cover. The intermediate layers improve the playing characteristics of solid balls, and can be composed of thermoset or thermoplastic materials.
Typically, solid golf ball cores are spherical and solid. In an effort to improve the playing characteristics of balls, typically the golf ball core diameter or core compression has been varied. It is desired to provide a solid golf ball with an improved core that provides unique performance characteristics.
Several patents have been issued which are directed towards modifying the geometry of various golf balls and components thereof.
Several patents are directed to spherical cores that have been modified with features such as bores or projections. U.S. Pat. No. 2,364,955 issued to Diddel, for example, discloses a golf ball that has a spherical core with radially extending bores. The bores are filled with a frangible material. Then the core is encased in a cover. On impact the frangible material breaks in order to absorb the impact energy. By absorbing this energy, the invention is supposed to decrease the rebound or resilience of the ball and provide a short distance ball. As a result, it is stated smaller golf courses may be used.
U.S. Pat. No. 720,852 issued to Smith discloses an internal core with a spherical surface that includes small, solid protuberances projecting therefrom. The core is encased in a rubber layer having small, solid protuberances projecting therefrom. A silk layer is wound thereon, then the ball is encased in an outer covering. The purpose of the core protuberances is to allow good anchorage for the rubber and silk layers and to increase the resiliency of the ball as a whole.
In other instances hollow, spherical cores are used. For example, U.S. Pat. No. 1,524,171 issued to Chatfield discloses a core with a hollow, spherical center that supports cylindrical, solid lugs. A spherical casing surrounds and abuts the tips of the lugs. The lugs and casing are designed so that the casing compresses the lugs in the finished ball. Fluid or wound rubber bands occupy the space around the lugs, between the spherical center and the casing. The lugs are meant to promote accurate location of the center by facilitating uniform and spherical winding of the rubber bands about the center. An outer shell surrounds the casing.
U.K. Pat. Application No. 2,162,072 issued to Slater discloses a golf ball with an inner core that includes a plurality of solid, support members or struts that diverge from a common center. The struts form a generally cubic, tetrahedral, or octahedral shaped core. The struts serve to locate the inner core symmetrically within a mold cavity. An outer core is molded about the inner core, and a cover is molded thereon.
U.S. Pat. No. 5,480,143 issued to McMurry discloses a substantially spherical practice ball comprising mutually perpendicular members with a plurality of walls that interconnect the members. The walls are for increasing the drag on the ball so that smaller playing fields can be used.
U.S. Pat. No. 5,836,834 issued to Masutani et al. discloses a two or three piece golf ball comprising a two-layer solid core composed of a low-hardness inner core and a high-hardness outer core joined around the low-hardness inner core. A projection is formed on the inner surface of the high-hardness outer core such that the projection extends along an approximate normal direction, while a depression corresponding to the projection is formed in the outer surface of the low-hardness inner core, and the low-hardness inner core and the high-hardness outer core are joined together such that the projection is inserted into the depression.
However, these patents do not disclose a golf ball having the configuration as disclosed herein to provide the improved golf balls of the present invention.
The present invention is directed to a golf ball having a core geometry designed to provide improved playing characteristics such as spin rate, initial velocity, compression, and feel.
The golf ball comprises an inner core, an outer core surrounding the inner core, and a cover encasing the cores. The inner core is one piece with a plurality of projections extending from a center portion. The solid or non-wound outer core is disposed around the projections so that the outer surface of the outer core is spherical to form a non-wound core. The inner core is formed of a first material and the outer core is formed of a second material. These materials have substantially different Shore D hardnesses, elastic modulii, specific gravities, or Bayshore resiliences. The cover may include one or more layers.
In one embodiment, the inner core includes a central portion and a plurality of spaced projections extending radially therefrom such that they form substantially a spheroid. In one embodiment, the projections are conical, and the projections include a base adjacent the outer surface of the central portion. The base is greater than or equal to the height of each projection.
In yet another embodiment, the inner core includes a central portion and a plurality of projections that have enlarged free ends which can define recesses for receiving material.
In another embodiment, the inner core is shaped like a spheroid and thus includes a substantially spherical outer surface including a plurality of projections and adjacent indentations. The projections have a maximum length greater than a maximum width. The outer core is disposed within the indentations and surrounding the inner core.
In another embodiment, the golf ball includes an inner core radius that includes only inner core material and an outer core radius that includes both inner and outer core material. The inner core and outer core volumes are calculated using the respective radius, and a transition volume is the difference between the two volumes. The golf ball in one embodiment is formed with a transition volume of at least about 10% of the outer core volume.
In one embodiment of the golf ball of the present invention, the elastic properties of the ball are such that the inner core and outer core materials are selected to satisfy the relationship below. When a first sample is formed of inner core material, a load can be applied to the sample and under the load the sample deflects so that a first ratio of the load over the sample deflection is measured. When a second sample is formed of the outer core material, a load can be applied to the sample and under the load the sample deflects so that a second ratio of the load over the sample deflection is measured. The inner and outer core materials should be selected so that the difference between the first and second ratios are at least about 10%.
The relationship between the outer core and the inner core are such that the ball has various playing characteristics at various club impact speeds.